Horn was listed as critical Saturday, according to the University Medical Center for emergency surgery's recorded message service, updated at 2:30 a.m. (5:30 a.m. ET).

The tiger lunged at Horn's neck about half-way through the show, and dragged him off stage, audience members said. "He looked like a rag doll in his mouth," said Kirk Baser, from Pennsylvania.

Emergency officials arrived at the MGM Mirage Hotel-Casino around 8:20 p.m. and treated Horn for massive blood loss before he was rushed to University Medical Center for emergency surgery.

Horn was talking at the time emergency workers arrived, but had trouble breathing, Clark County Fire spokesman Bob Leinbach said.

Horn, the darker-haired member of Siegfried & Roy, was born in Nordenham, Germany on October 3, 1944. Combining magic with tiger stunts, the flamboyant duo has performed on the Las Vegas strip for nearly 30 years.

Tiger in quarantine

The tiger that attacked Horn is currently in quarantine and no one else was injured in the attack, according to MGM Mirage spokesman Alan Feldman.

Comedian Penn Jillette of the duo Penn & Teller visited the hospital Saturday afternoon to show support for his long-time friends and find out more about Horn's condition, he said.

"It's really not good," Jillette told reporters. "I mean, when I talked to Siegfried last night, he said, you know, it was going to be OK. You have no idea what that means. It means a friend that he's loved dearly and worked with for 28 years -- his heart's still beating, and there's still hope."

Jillette said Horn had always worked well with the big cats on stage.

"Every living thing goes crazy. Every species," he said. "And there's nothing -- no fingers to point. There's nothing. It's just a really bad thing happening to a really important, wonderful, very, very strong guy. I mean his strength is breathtaking."

Audience members shocked

Audience members were shocked to realize the attack was not part of an illusion or magic trick.

Amy Sherman, who was sitting in the front row with her mother about 10 yards away from the stage, said the attack happened right after Horn introduced the tiger.

"Right after that, the tiger kind of turned its head and bit him on the arm," Sherman said. "Roy started taking a microphone and started whapping the tiger on the head."

The tiger, who was on a short leash, then dragged Horn to the ground and they struggled before the tiger dragged him behind a curtain by his neck, she said. Trainers on stage rushed to aid Horn, trying to subdue the tiger.

"We just heard all this commotion behind the curtain and you could hear Roy scream," Sherman said. "Everyone at our table was kind of looking at each other, like 'Oh my God,'" she said.

After about a minute, which Sherman's mother said seemed like forever, Siegfried appeared on stage.

"You could tell he was really shook up, and he just said, 'I'm sorry but the show is over, and you know, the show has been canceled'" Joyce Edenholl said.

"Everyone there I think , thought it was part of the act, because no one really freaked out," Kirk Baser said. "When it grabbed him and dragged him off the stage, I thought maybe it was like some magic trick where they switch a rag doll or something."

A group of Australians said they witnessed the attack from the front row of the crowded theater, and also thought it was just part of the show.

"A lady ran past me, freaking out and it was then I sort of, in the back of my mind, thought now this isn't part of the show," said David Strudwick. "And then you look at the staff and they had a bit of horror in their eyes and ... it was like, wait a second, it may not be a part of the show."